Acoustic device



Sept. 16, 1930.

J. v. L. H OGAN ACOUSTIC DEVICE Filed Jan. 30, 1926 FAD/0 W4 VES MODUZ/ITOB (5 fic gvsmon' is as 'a so-called pick up or Patented Sept. 16, 1930 JOHN V. L. HQGAN, 01E FOREST HILLS; NEW YORK, assrenon 'ro RADIO mvmrrrons,

11m, asconrona'rron or new YORK soonsrro DEVICE Application filed January 30, 1926. Serial No. 85,069.

acoustic frequencies, whereby the fidelity of transformation of complex or simple sounds having a great variety of frequencies may be improved. Further objects are to attain a high degree of uniformity of space dlstribution of the effects involved, and to produce a device both simple in manufacture and simple and reliable in use.

' One of the largest uses for such a device is as a reproducer or so-called loud speaker for the conversion of audio frequency electric currents into mechanical vibrations in a relatively dense medium, such as an iron armature, and the transfer of these vibrations to a less dense medium such as air. Another use telephone transmitter device, in which air Waves of sound frequencies are caused to produce similar mechanical vibrations in a relatively dense medium and these vibrations act in the system to produce or cause electric currents having similar variation frequencies. Such electric currents may be used for a variety of purvibration-transfer devices as poses, such as (1) the operation'of a telephone, receiver or other reproducer, (2) the modulation of ultra-audible electric currents in a radio or carrier current line telephone system, or (3) the operation of a phonograph-record cutting device for the recordin of sound or other vibrations.

caring in mind the various uses 0 such that which I have invented, together with the fact that much the same criteria of excellence apply to the performance of thesystem in any of its uses, the discussion of this invention may be simplified by considering the structure from the viewpoint of converting audio frequency currents to sound waves in air. This is the function of the loud-speaker so largely used in connection with radio telephone receiving apparatus.

I have discovered that in order to convert electric currents into equivalent sound waves with the highest degree of effectiveness, both as to quality of reproduction and volume of tone, the following criteria should be met:

(1) The efliciency of the reproducer, measured by the ratio of sound wave energy produced to electric wave energy applied at any instant should be a maximum.

(2) The efficiency as above defined should be a constant quantity as a function of frequency throughout the useful sound range o say 25 to' 10000 cycles.

(3) The efficiency, tween the efliciencies at various frequencies, should remain constant as the vibration varies.

- (4) Provision should be made .for free v1- bration of the moving system through the maximum amplitude desired.

(5) The distribution of the sound effect should be as nearly spherical as possible.

As to the first criterion set forth above, one of the greatest problems has been to apply the mechanical forces produced by the (usualair by the use of a megaphonic horn, but such practice violates the second. requirement above for the reason that the horn or equiva-- lent sound passage in general introduces conditions that prevent 'a uniform efliciency over a wide band of acoustic frequencies.

The second criterion is of the maximum importance, for upon it depends the fidelity of reproduction or conversion of sounds covering the audible range. To attain substantial perfection of conversion the relations of effective inertia, mechanical restoring force and mechanical damping should be so chosen that operation at no one frequency within the operating range is favored (in the production of response) above any other /frequency in that range. Preferably the mechanicalperiods introduced by inertia and restoring force should be lower than 1/25 second or higher than 1/10000 second, or their efiects amplitude of should be minimized by high damping in the unless it is met the're be a difference in the fidelity of'production of or response to ment that ,stantially com sound waves aving'diflerent intensities.

The fourth criterion needs no extended discussion, since*"'it is simply a design requireprevents the production, by the de-' vice itself, of foreign noises such as buzz'es ordscra'tches when operating at high amplitu es.

The fifth criterion is of having a direct bearing upon the practical value of the device. Horn type reproducers have a substantially conical sound distribution, the diameter of the section of the cone being relativelysmall compared to the dis-- tance of the section from 'the diaphragm. Other reproducers-of the prior art, utilizing enlarged lane or conical diaphragms, also have distribution patterns that are in general conical, though the section-diameter distance ratio is greater than in the cases where horns are used. With all these prior art reproducers, however, there are large volumes of the surroundlng space where the sound effect is a m1n1mum,as for instance in the plane of the enlarged diaphragm or cone or behind the orifice of the horn.

y my invention I can combine the five controlling criteria of a perfect sound or v'ibratlon converting device in such a waythat they are more fully attained than in any prior art device of which I have knowledge.

The invention may be understood from the following description taken in connection with the drawing, in which p Fig. 1 shows, partially in section, emb

Fig. 2 ture.

Fig. producer-of received radio sign 4 illustrates the device used as a pickup or radio telephonic transmission. I

Referring specifically to Fig. 1, the element 5 is a relatively flexible or resilient and sublete sphere of celluloid, paper or other 'suita 1e material. This surface is preferably substantially homogeneous in great importance,

a simple ent containmg the lnvent'ion. shows in section a preferred struc- 3 illustrates the device used as a reals.

. structure, although when some materials such as paper are used the sphere may be construc'ted of gored sections united in orange peel fashion and preferably with the ioints or overlaps between gores running longitudlnally from pole to pole. It is supported at one pole by a relatively rigid or xe'd membet 6 and at the antipodal pole carries a link 7 suitably attached (as by means of a pair of cup-shaped washers 88 and clamp nuts 9 -9). The .link or drive-rod 7 extends to a 10 which is arrangedto act upon or be acted upon by an electro-magnetic system including the coil 11 with terminals 12, 13, the pole piece 14 (which is preferably laminated) and the polarizing magnet 15. a

It will be understood that the structure of Fig. 1 is not complete in' detail, but that the drawing is intended to illustrate certain special features of the invention. In practice a number of modifications are desirable, such as the substitution of a bipolar polarized magnetic system with pivoted armature or a driving coll magnetic field forfthe simple system shown.

In operating the device as a reproducer the {alternating or pulsating currents representing t e sounds to be generated are applied to the coil 11 via its terminals 12-43.

The polarizing magnet 15 acting upon the.

armature 10 places? the speaking sphere 5 under a definite initial axial stress tending to 7 is moved axially. These vibrations tend.

to change the body 5 from an approzn'mately true sphereto a prolate spheroid of varying length, or if a magnetic system producing compression upon the sphere is used the forms assumed in action may include that of an oblate spheroid'. The changes of form produced by the driving current result in substantially similar of the surface of the sphere, such movements having a substantial radial component and resulting in a movement of air molecules in contact with the surface to produce the,de sired sound waves which pass off in all directions.

In usingv the device as a sound pick-up the reverse 0 ole of operations takes place. Sound waves impinging uponjhe surface of the sphere-from any direction cause it to move, the motions resulting in an axial motion of the push. rod 7 and consequent variations in the air gap between armature 10 and pole-piece 14. These variations produce correspondingalternating electromotive forces in the coil 11, and current conveying such variations may be led away by means of terminals 12 -13.

Itwill be observed that the production of sound by this device involves a symmetrical operation and that the generated sound waves may be expected to pass outward, from the sphere inall directions with substantiall uniform .or at least an extremely wide e fective distribution. When used as a pickup, however, sopnd waves are often applied suspended so as to move in an annular space across which exists a radial and equal movements f ll trically as desired tral music) from a single direction, so tending to cause an unsymmetrical movement of the sphere. In such cases it may be noted that the pickup from certain directions (and in particular along the axial line) may be somewhat more eflicient than that from other directions. This feature may be utilized by turning the sphere as desired, and in the interception of complex multiple sound waves (as in orchesmay be availed of for equalizing or controlling the electrical response to sound waves from various points or directions.

It will be understood that the movements referred to, and the consequent changes of form of the vibrating sphere, may be very minute in magnitude. Efiective sound waves of large intensity may be generated by (or may result in) motions that are almost of microscopic size.

In Fig. 2 the sphere 5 is supported at one pole by the pedestal 16, a hole in the sphere being cut to permit the push-rod 7 to extend to the antipodal pole at 17. The lower end of the push-rod is attached to the electromagnetic system 18, whose driving coil terminals are brought out to the insulated binding posts 19 and 20. The operation of the device in this form is as described in connection with Fig. 1. For the magnetic system I prefer the moving coil type above referred to.

Fig. 3 shows a receiving antenna and ground system 21-22 passing through a tuner and detector 23, whose output is connected to an audio amplifier 24:. The audio frequency electric power delivered from the amplifier passes to the reproducer 25, which may be of the form shown in Fig. 1 or Fig. 2.

Fig. 4 shows the device 25 operating as a pick-up, in which case its terminals may be connected to an audio amplifier 26. The output of this amplifier may be conveyed elecby means of line wires 27, to a radio telephone transmitting station comprising audio amplifier 28 and modula tor-oscillator 29. The modulated radio frequency currents produced by 29 may be led to a radiating antenna-ground system 3031, from which radio waves are transmitted.

Although I have shown and described the vibrating surface of my acoustic device as a sphere, Iwish it understood that the surface need not be mathematically or even practically spherical in order to obtain many of the advantages of the invention. An oblate or a prolate spheroid, for instance, may be satisfactorily used and other variations in form which do not depart from the spirit of the invention as expressed in the appended claims will occur to the user. In general the vibrating body is preferably a substantially closed envelope with respect to the main acactive surfaces, though it will be understood that orifices may be provided for entrance of the drive-rod, insertionof the magnetic driving unit, provision of pressure nodes. to minimize air-chamber resonant periods where they occur at dlsturbmg frequencles, etc.

Neither do I wish to be understood as limita ing my invention to the specific forms shown, for many modifications of structure as to the supporting and driving mechanism may obviously be made. For example the push-rod 7 may be replaced by a practically inertialess filament under tension, or may be shortened by placing the magnetic system 18 partly or entirely within the surface 5. The magnetic system may be centrally supported within the sphere, and the vibrating surface suspended upon two oppositely-acting drive-rods so that mechanical vibrations are applied directly and in opposing directions to both antipodal polar points. Where the reproduction of phonographically recorded sounds. is desired the mechanical vibrations caused by the record may be applied directly to the push-rod or its equivalent without the interposition in the system of electro-mechanical means.

What I claim is:

1. An acoustic device comprising a substantially spherical non-metallic wall of paperlike material, the polar dimension of which is adapted to increase and decrease simultaneously wit-h equatorial contraction and expansion in combination with a support at one point of said wall and an electromagnetic system comprising a movable element connected mechanically to another point of said wall incombination with a support for said device at one pole thereof and vibrating means connected to the opposite pole.

2. An acoustic device comprising a substantially spherical wall of inelastic material having substantially uniform thick ness and flexibility in combination with a support at one point of said wall and an electromagnetic system comprising a movable element connected mechanically to another point of said wall in combination with a support for said device at one pole thereof and, vibrating means connected to the op posite pole.

3. An acoustic device comprising a substantially spherical homogeneous formable as a whole in combination with a support at one point of said body and an body de- 4. An acoustic device comprising an approximately spherical body formed entirely of non-magnetic material in combination with a support at one point of said body and an electromagnetic system comprising a movable element connected mechanically to another point of said body in combination with a support for said device at one pole thereof and vibrating means connected to 1 the opposite pole.

5. A hollow spherical acoustic device of non-metallic inelastic material subjected to the opposite balanced'in-ternal and external air pressures in combination with a support at one point and an electromagnetic system comprising a movable element connected mechanically to another point in combination with a support for said device at one pole thereof and vilirating means connected to the opposite o e. p 6. A hollow approximately spherical acousticdevice composed of segmental areas of non-metallic material of approximately uniform thickness united along polar great circles in combination with a support at one point and an electromagnetic system comprising a movable element connected mechanically to another point in combination with a support for said device at one ole thereof and'vibrating means connecte to the opposite pole. K

7. hollow approximately spherical acoustic device equatorially deformable, means for supporting said device at one pole, and means for applying power axially at pole to increase and decrease its polar dimension, said means comprising a support for said spherical device and an electromagnetic system mechanically connected to said device.

An acoustic device comprising a substantially spherical wall, mechanical connections thereto. at substantially diametric portions-thereof, said wall being supported by said mechanical connections only, whereby said wall is capable of free movement at i all points remote from said connections.

JOHN V. L. HOGJ AN. 

